Question: On the first 3 quizzes of her history class, Umaima got an average score of 84. What does she need on the next quiz to have an overall average of 86?
Solution: Let her score on the next quiz be $x$ The sum of all of her scores is then $3 \cdot 84 + x$ The same sum must also be equal to $4 \cdot 86$ Solve: $x = 4 \cdot 86 - 3 \cdot 84 = 92$.